This class just automates the basic pattern of having a form that, when submitted, should send its data to the server via Ajax and take whatever comes back and inject it into a DOM element.
new Fupdate($('fupdateForm'), $('fupdateReply'));

That's pretty much all you gotta do.
I know - "Fupdate" (Form Update abbr.) is kinda lame, but I really couldn't come up with a better name... BTW, it's pronounced as one word (not "F-Update"; rather "fupdate"). I'm open to suggestions!